Composition and crystallization of milk fat fractions

Milk fat was fractionated by solvent (acetone) fractionation and dry fractionation. Based on their fatty acid and acyl-carbon profiles, the fractions could be divided into three main groups: high-melting triglycerides (HMT), middle-melting triglycerides (MMT), and low-melting triglycerides (LMT). HMT fractions were enriched in long-chain fatty acids, and reduced in short-chain fatty acids and unsaturated fatty acids. The MMT fractions were enriched in long-chain fatty acids, and reduced in unsaturated fatty acids. The LMT fractions were reduced in long-chain fatty acids, and enriched in short-chain fatty acids and unsaturated fatty acids. Crystallization of these fractions was studied by differential scanning calorimetry and X-ray diffraction techniques. In this study, the stable crystal form appeared to be the β′-form for all fractions. At sufficiently low temperature (different for each fraction), the β′-form is preceded by crystallization in the metastable α-form. An important difference between the fractions is the rate of crystallization in the β′-form, which proceeds at a much lower rate for the lower-melting fat fractions than for the higher-melting fat fractions. This may be due to the much lower affinity for crystallization of the lower-melting fractions, due to the less favorable molecular geometry for packing in the β′-crystal lattice.     

Thermal analysis of palm mid-fraction,cocoa butter and milk fat blends by differential scanning calorimetry

Commercial samples of anhydrous milk fat (AMF), Ivory Coast cocoa butter (CB) and palm mid-fraction (PMF) were blended in a ternary system. The melting characteristics of the blends were studied by differential scanning calorimetry (DSC). Results suggest that in the studies of interaction involving more than two fats, partial area (A_i) under the melting peak should be converted to partial enthalpy (ΔH_i) rather than to solid fat index. The ΔH values of the blends decreased as the amount of AMF was increased and increased as the amount of CB was increased. In general, the effect of PMF was less pronounced compared to the effect of the other two fats. Eutectic effects within the ternary system could be detected by measuring the deviation of melting enthalpy by DSC, and from the corresponding values that were calculated for the thermodynamically ideal blends. The deviation reached a maximum when the amount of AMF was about 33%. On the binary line of CB/PMF, the eutectic effect was maximum at about 50–75% PMF. The interaction effect in the system was more noticeable at 30 and 20°C than at lower temperatures. Evaluation at 30°C was preferred because both the effect of AMF in the ternary system and the effect of PMF on the binary line were more readily observed.     

Highly efficient nucleating additive for isotactic polypropylene studied by differential scanning calorimetry

The influence of an organic phosphate derivative in the crystallization of the monoclinic phase of isotactic polypropylene was studied by differential scanning calorimetry. To analyze the nucleation activity of the additive, the self‐nucleation process of the pure polymer was also studied by thermal techniques. A large increase in crystallization temperatures was obtained even for the lowest concentration of the additive, and its nucleating efficiency is the highest observed for α‐nucleating agents in isotactic polypropylene. The nucleating agent was also observed to increase the stability of the crystals formed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1669–1679, 2002; DOI 10.1002/app.10546     

Determination of the predominant polymorphic form of mango (Mangifera indica) almond fat by differential scanning calorimetry and X‐ray diffraction

In this paper, some important properties, from the application point of view, of mango (Mangifera indica) almond fat var. Manila (MAF) were analyzed by differential scanning calorimetry and X‐ray diffraction techniques. The thermal profile, the solid fat content (SFC) and the predominant polymorphism of MAF samples, previously characterized chemically, were studied. The results showed that this fat, from one of the main residues of mango industrialization, had a relatively simple fusion/crystallization behavior. Stabilized samples showed a simple SFC profile with one marked slope between 35 and 40 °C. Different thermal histories demonstrated the existence of at least four polymorphs. The non‐stabilized samples corresponded predominantly to the formation of the crystalline &α form. The stabilized samples, tested under several time and temperature conditions, allowed the formation of two other polymorphs, which are both unstable forms and were formed during &α to β polymorphic transition. The X‐ray diffraction information confirmed the presence of the less and more stable MAF polymorphs, allowing us to conclude that MAF is a β‐stable fat, just as is cocoa butter.     

Thermal memory of polyethylenes analyzed by temperature modulated differential scanning calorimetry

Temperature modulated differential scanning calorimetry (TMDSC) was employed to study the melting and crystallization behavior of various polyethylenes (PEs). Samples of high density PE (HDPE), low density PE (LDPE), linear low density PE (LLDPE), and very low density PE (VLDPE) with different crystal structures and morphologies were prepared by various thermal treatments (isothermal crystallization and slow, fast, and dynamic cooling). The reversing and nonreversing contributions, measured on the experimental time scale, were varied, depending on the crystal stability. A relatively large reversing melt contribution occurs for unstable crystals formed by fast cooling compared to those from slow cooling treatments. All samples of highly branched LDPE, LLDPE, and VLDPE showed a broad exotherm before the main melting peak in the nonreversing curve, suggesting crystallization and annealing of crystals to more stable forms. Other samples of HDPE, except when cooled quickly, did not show any significant crystallization and annealing before melting. The crystallinity indicated that dynamically cooled polymers were much more crystalline, which can be attributed to crystal perfection at the lamellar surface. A reversible melting component was also detected during the quasiisothermal TMDSC measurements. Melting is often accompanied by large irreversible effects, such as crystallization and annealing, where the crystals are not at equilibrium. Such phenomena during a TMDSC scan provide information on the polymer thermal history. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 681–692, 2003     

Detection of animal fats in butter by differential scanning calorimetry: A pilot study

Because of its high price, butter has always been the object of adulteration by addition of less expensive vegetable or animal fats. Although a number of methods have been proposed for the detection of butterfat adulteration, none has found widespread use. For this reason, a study was conduced to assess the use of differential scanning calorimetry (DSC) for detecting the presence of added animal fat, i.e., chicken fat, in butter. The results obtained show that DSC is an efficient method for characterizing pure animal fats as well as their mixtures. Furthermore, the accuracy with which data are obtained, in combination with the sensitivity of DSC to subtle changes in chemical composition of the sample, makes DSC an attractive possibility for development as a quality control procedure.     

Cure kinetics of epoxy resins by differential scanning calorimetry technique

The curing reactions of epoxy resins with aliphatic amine are investigated using the differential scanning calorimetry technique with a single dynamic scan. The rate of the reaction was followed over the temperature range 30–250°C, and the activation energy and the order of the reaction are determined using four different computational methods. The activation energy for the various epoxy systems is observed in the range 40–76 kJ mol^?1 and the order of the reaction is observed to be ? 1·0.     

Thermogravimetry and differential scanning calorimetry of Kentucky bituminous coals

A detailed investigation has been made of the thermal characteristics of six Kentucky bituminous coals undergoing pyrolysis in an inert atmosphere at three different heating rates. The specific heats of the coals and the enthalpy changes characterizing their thermal degradation were measured by differential scanning calorimetry. Thermogravimetry was employed to measure the attendant weight changes, which were used to normalize the heat flow data to unit sample weight, enabling a quantitative comparison of the thermal behaviour of the several coals. The specific heats of the dry coals lie in the range 1.21–1.47 J gK^?1, 100–300 °C. The exothermic heat flow from 300 to 550 °C, where the major weight loss occurs, has been associated with the primary carbonization process, the development of the plastic state, and the onset of secondary gasification, which is responsible for coke formation. In the high pyritic sulphur coals, the endothermic pyrite/pyrrhotite transformation at ≈580 °C is clearly defined. A preliminary global kinetic analysis of the thermogravimetric data has been made, using a modified Kissinger equation at the maximum rate of weight loss. Activation energy and pre-exponential factor values of the order 198–220 kJ mol ^?1 and 2–85×10¹²s^?1 have been obtained. These compare well with the limited published values for similar coals.     

Distribution of lamella thicknesses in isothermally crystallized polypropylene and polyethylene by differential scanning calorimetry

The procedure for obtaining lamellar thickness distribution from differential scanning calorimetry (d.s.c.) curves is presented. The method has been used to study melt-crystallized polypropylene and polyethylene. The melting of the samples as registered by d.s.c. has been analysed and information regarding lamellae thickness is presented. The results obtained were consistent with the thicknesses of lamellar crystallites derived from small-angle X-ray scattering (SAXS) patterns.     

Rigid amorphous phase and low temperature melting endotherm of poly(ethylene terephthalate) studied by modulated differential scanning calorimetry

The rigid amorphous phase, the low temperature melting endotherm, and their development with thermal treatment in poly(ethylene terephthalate) (PET) were investigated by means of modulated differential scanning calorimetry. The differential of the reversing heat capacity and nonreversing heat flow signals were used to analyze the behavior of the glass transition and the low temperature melting endotherm. With increasing annealing time, the increment of the heat capacity at the glass‐transition temperature decreased and the increment of heat capacity at the annealing temperature increased. It was suggested that the origin of the low temperature melting endotherm mainly resulted from the transition of the rigid amorphous fraction for the PET used. The glasslike transition of the rigid amorphous fraction occurred between the glass transition and melting. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2779–2785, 2001     

Characterization of the thermal properties of PLA fibers by modulated differential scanning calorimetry

Polylactide (PLA) has been melt spun to produce multifilament continuous yarns. The thermal characteristics of PLA filaments have been investigated using modulated differential scanning calorimetry (MDSC). With MDSC, it is possible to separate the different thermal events and to analyze them more precisely. The influence of hot drawing on thermal properties of PLA filaments has been studied. Hot drawing promotes an increase of glass transition temperature (T_g) and a decrease of heat capacity. The cold crystallization spreads on a larger range of temperature and the peak occurs at a lower temperature. The initial degrees of cristallinity of PLA filaments have been calculated thanks to the reversing and non reversing curves of MDSC. Tensile properties of PLA filaments are also investigated.     

PET切片熔点差示扫描量热法测试的改进

针对PET熔点测试差示扫描量热法曲线中出现的熔融峰上的峰干扰,从热历史的研究和消除进行实验,找出了方法中所规定的测试熔融最高温度不能完全消除一些样品的热历史问题,并多方引证对消除热历史的熔融温度及方法的改进提出了建议。     

Differential scanning calorimetry of water buffalo and cow milk fat in mozzarella cheese

The thermal profiles of the fat in mozzarella cheeses made from cow milk (CM) and water buffalo milk (WBM) were obtained by differential scanning calorimetry (DSC). The DSC curves of mozzarella cheese made from WBM were distinguishable from those of CM. The curves resembled those of the corresponding milk fats and could be divided into low-, medium-, and high-temperature melting regions. The valley in the curve between the low- and medium-temperature melting regions was at 10.8°C in WBM cheese and below 10°C in CM cheese. In the WBM cheese, the area of the low-melting region was larger than the area of the medium-temperature melting region, but the two areas were equal in the CM cheeses. Mixtures of the two cheeses exhibited temperature and area values between those of the pure cheeses. Milk-fat mixtures showed similar behavior. The contrasting DSC melting profiles provide a way of distinguishing between the two mozzarella cheese types and for detecting mixtures of the two fats in mozzarella cheese.     

Detection of lard and randomized lard as adulterants in refined-bleached-deodorized palm oil by differential scanning calorimetry

A study was conducted to assess the use of differential scanning calorimetry (DSC) for detecting the presence of lard/randomized lard as adulterants in refined-bleached-deodorized (RBD) palm oil. Lard extracted from the adipose tissues of pig was chemically interesterified using sodium methoxide as catalyst. DSC thermal profiles of both genuine lard and randomized lard were compared with those of other common animal fats such as beef tallow, mutton tallow, and chicken fat. Lard and randomized lard were then blended with RBD palm oil in two series, in proportions ranging from 0.2 to 20%, and DSC analyses were obtained. The DSC cooling profiles of adulterated RBD palm oil samples showed an adulteration peak corresponding to lard/randomized lard in the low-temperature region. This peak was confirmed as an indicator of the presence of lard in RBD palm oil since similar experiments carried out using other common animal fats such as mutton tallow, beef tallow, and chicken fat showed that the lard adulteration peak could be distinctly identified. Using this method, a detection limit of 1% lard/randomized lard was reached (P<0.0001).     

Studies on heat capacity of cellulose and lignin by differential scanning calorimetry

Heat capacities (C_p) of wood cellulose, other natural celluloses having various crystallinities and of lignin are given for temperatures ranging from 330K to 450K using differential scanning calorimetry. The calculation of the C_p of completely crystalline cellulose is based on a two-state model of cellulose which assumes linearity between the crystallinity and C_p. The higher C_p found in the amorphous region compared with the crystalline region, is apparantly due to differences in the frequency of molecular vibration in these two areas. The glass transition of lignin was observed as a sudden increase in C_p at 400K. The precise T_g of lignin was dependent on the sample's origin, characterization, thermal history etc. When annealed at around T_g enthalpy relaxation occurs, and this can be detected as an endothermic peak in the C_p curve at the transition temperature. Moreover, the C_p in the glassy state was found to decrease with both annealing time and temperature, suggesting that rearrangement of the local conformation of lignin molecules occurs in the glassy state temperature range.     

Modulated temperature differential scanning calorimetry for examination of tristearin polymorphism: 2. Isothermal crystallization of metastable forms

The transformations of tristearin were examined by modulated temperature differential scanning calorimetry (MTDSC) in order to examine the utility of this technique. Tristearin has been used as a model polymorphic system, showing metastable phases and complicated transformation routes occuring at relatively slow rates. The β′-forms generated by thermal treatment under modulation do not differ significantly from those generated by the corresponding treatment without modulation. While the total heat flow thermograms are similar, the deconvoluted reversing component shows that annealing, especially at 63°C, has a significant effect on the crystal size and perfection of the solid phases formed. MTDSC also enables the melting of β′ to be separated from the simultaneous crystallization of the β form as evidenced in the c _p component. Quantitative interpretations about such systems cannot be drawn from MTDSC at this point in time.     

Crystallisation and melting behaviour of palm kernel oil and related products by differential scanning calorimetry

Lauric oils are valuable sources for oils suitable for various food applications. They are particularly useful as cocoa butter substitutes for which steep solid fat content profiles are required. Palm kernel oil is one such fat, which upon fractionation and/or hydro‐genation provides a variety of oil fractions with different oil composition and properties. The stearins have excellent properties for confectionery fats, while the oleins can be further hydrogenated to improve their properties. This paper gives an overview of the properties of products of palm kernel oil, produced from fractionation and hydrogena‐tion. The melting and crystallisation properties from differential scanning calorimetry studies are discussed in relation to the triacylglycerols of the oils.     

Study of melting and crystallization behavior of polyacrylonitrile using ultrafast differential scanning calorimetry

The thermal behavior of polyacrylonitrile (PAN) has been investigated using X-ray diffraction, differential scanning calorimetry (DSC), and ultrafast DSC. In conventional DSC, it is difficult to prevent the concurrent occurrence of the exothermic reactions of PAN with melting. However, in the ultrafast DSC curve, the exothermic peak due to these reactions disappears over the temperature range 0–400 °C at heating rates above 250 °C s⁻¹. Alternatively, the glass transition and the melting of PAN are observed over the temperature range 109–129 °C and 335–362 °C, respectively. Moreover, upon cooling from the molten state at a rate of −7500 °C s⁻¹, PAN crystallization is observed at 204 °C. These findings were observed repeatedly during heating and cooling measurements. From the extrapolation analysis, the zero-entropy-production melting temperature of PAN is found to lie in the temperature range 320–350 °C. Finally, the equilibrium melting temperature of PAN is estimated to be ca. 465 °C.